The subject matter disclosed herein relates generally to a pulse detonation tube and, more specifically, to enhancing the durability of the pulse detonation tube by employing a local flexural wave modifying feature.
Pulse detonation combustion can be utilized in various practical engine applications. An example of such an application is the development of a pulse detonation engine (PDE) where hot detonation products are directed through an exit nozzle to generate thrust for aerospace propulsion. Pulse detonation engines that include multiple combustor chambers are sometimes referred to as a “multi-tube” configuration for a pulse detonation engine. Another example is the development of a “hybrid” engine that uses both conventional gas turbine engine technology and pulse detonation (PD) technology to enhance operational efficiency. Such pulse detonation turbine engines (PDTE) can be used for aircraft propulsion or as a means to generate power in ground-based power generation systems.
Within a pulse detonation tube, the combustion reaction is a detonation wave that moves at supersonic speed, thereby increasing the efficiency of the combustion process as compared to subsonic deflagration combustion. Specifically, air and fuel are typically injected into the pulse detonation tube in discrete pulses. The fuel-air mixture is then detonated by an ignition source, thereby establishing a detonation wave that propagates downstream through the tube at a supersonic velocity. In addition, a weaker shock wave may propagate upstream toward the combustor inlet. The detonation process produces pressurized exhaust gas within the pulse detonation tube that may be used to produce thrust or be converted to work in a turbine.
As will be appreciated, material properties and geometry of the pulse detonation tube at least partially define a speed at which mechanical waves travel through the structure of the tube. This speed may be known as the flexural wave speed and may include a breathing mode component and a dilatation component. As the detonation wave travels through the tube, the sharp pressure rise associated with the detonation wave front generates a mechanical wave at each discrete location along the length of the tube. These mechanical waves propagate through the tube structure at the flexural wave speed. If the speed of the detonation wave is substantially similar to the flexural wave speed of the tube, the detonation wave will excite the pulse detonation tube at resonance. Consequently, the strain resulting from the detonation wave will be significantly greater than the strain associated with static pressure loading at the detonation wave pressure. Such strain amplification may increase along the length of the tube due to the additive effect of multiple coalescing flexural waves. For example, in certain tube configurations, the strain may be amplified by a factor of 2, 3, 4, 5, 6, or more compared to static pressure loading. As a result, the longevity of the pulse detonation tube may be significantly reduced.